Plating bath containing formaldehyde producing material



United States Patent ice 3,185,637 PLATING BATH CONTAG FORMALDEHYDE PRODUCING MATERIAL Anthony Debs, 13203 Canterbury Road, Cleveland, Ohio No Drawing. Filed June 28, 1961, Ser. No. 120,207 2 Claims. (Cl. 204-55) This invention relates to the electrodeposition of copper, zinc and copper-zinc alloys and is particularly directed to an alkaline cyanide plating bath for depositing bright, mirror-like zinc and copper-zinc alloy deposits which contains a brightening agent as hereinafter described.

It is an object of the present invention to provide an aqueous alkaline cyanide plating bath for the deposition of zinc or copper-zinc alloy coating, the coating being materially brighter in surface appearance than ordinary Zinc coatings and having good ductility and leveling.

It is an object of the present invention to provide an improved plating bath and a method of using the same for electrolytically depositing zinc, copper and copperzinc alloys, the bath containing a brightening agent comprising a reaction product of formaldehyde and di cyandiamide.

' It is an object of the present invention to provide a plating bath for the electrolytic deposition of zinc from a cyanide plating bath by use of a brightening agent comprising a reaction product of dicyandiamide and formaldehyde.

It is an object of the present invention to provide a method of electrodepositing a metal such as zinc or a zinc copper-alloy from a plating bath in which a polymer of formaldehyde and dicyandiamide is used as a brightening agent.

It is an object of the present invention to provide a white brass or copper-Zinc alloy cyanide plating bath in which a polymer of'dicyandiamide and formaldehyde is used as the brightening agent.

The present invention provides an improved alkaline cyanide plating bath in which a polymer of a dicyandiamide and formaldehyde is used as a brightening agent.

A suitable material for the brightening agent of the present invention is a polymer of formaldehyde and dicyandiamide. The polymer is preferably made by reacting dicyandiam-ide, formaldehyde and boric acid in a mole ratio of 1, 3.5-5, and 01-1 moles, respectively, at about 70 to 100 C. for about three to four hours. The resultant polymer is a resinous liquid, is soluble in both hot and cold water and is non-precipitating even on extreme dilution of the aqueous solution. Its aqueous solution is stable in water on standing and, generally, the more boric acid used in making the polymer, the more stable the solution.

As pointed out in the US. Patent No. 2,852,490, which describes the preparation of a suitable dicy/formaldehyde/'boric acid polymer; the pH of the reaction solution generally should be initially below 7; the pH remains below 7 at first and, then, upon reaction of the ingredients, the pH of the solution rises and becomes practically constant.

While the polymer of dicyandiamide, formaldehyde and boric acid can be made with 1 to 5 moles of formaldehyde per mole of dicyandiamide, it has been found that only a 3.5 to 5 mole range gives solutions which are clear in cold water and stable. Upon standing, solutions of the polymers develop haziness and insolubility in cold water when only three moles of formaldehyde are used.

Continuing to describe the reaction, generally, the final pH is around 7 /2 to 8 /2 in a 10% solution.

Other suitable brightening agents, as effective as the dicy/ -formaldehyde/boric acid polymers, are condensation products of dicy, formaldehyde and formic acid. In these the reaction is not understood. They are produced by 3,185,537 Patented May 25, 1965 adding one mole dicy to 3 or more moles formic acid and then adding a mixture of 0.1 to 3 moles of formaldehyde to 1 to 4 moles of formic acid. The mixture is then refluxed at atmospheric pressure for several hours to several days and subsequently evacuated to a low pressure of the order of 20 mm. of mercury until the bulk of the formic acid has been evaporated out as determined by acidity tests. 4

To this mixture is then added cold very concentrated alkali hydroxide solution and the evaporation is continued until the solution becomes alkaline andbubbling and frothing cease. The product so formed has characteristics similar to those of the boric acid product but is also easier to control in a plating solution of alkaline zinc or zinc-copper alloy cyanide type.

A typical :bath for plating zinoin accordance with the present invention is given below in Table I, the table setting forth both the general ranges and the preferred ranges of each of the ingredients:

2 Percent by volume determined by trial in Hull cell.

As indicated above, generally about 0.005 to 2.5% by volume of the bath is generally the amount of brightening agent used. The 'brightener is the reaction product of dicyandiamide (sometimes called dicy), formaldehyde and boric acid. It is preferred that, for the best physical properties of the resultant coating such as density, fine grainness, low porosity, durability and brightness, a range of about ,4 to 2% by volume should be used although the best results are obtained with about 0.05 to 1.0 by volume of the bath. In any event, it has been found that when less than about 0.004% by volume of the brightener is used, there is little brightening effect and the coating is porous and of little commercial value. On the other hand, when more than 3.0% by volume of the polymer of dicy and formaldehyde is used, the resultant coating is irregular and becomes brittle an dark with increase of brightener.

The resultant coating from the above described zinc cyanide bath is a bright ductile zinc deposit requiring no bright dip.

If desired, the bath composition may be stabilized with a reaction product of salicylic acid and hexamethylene tetramine (sometimes called hexamine) using about /2 to 3 ounces per gal. of the above described reaction product. This reaction product generally contains a mixture of amino derivatives of salicylic acid.

Also in accordance with another aspect of the present invention, nickel and cobalt or mixtures thereof can be used in low free cyanide baths as such as those set forth in Table I. Nickel and cobalt may be added in the form of nickel or cobalt salts such as formates, carbonates, acetates, cyanides, chelates, or salts of nickel or cobalt and ethylene diamine or other poly amine in very small amounts, generally about 0.005 to 0.5 gram/liter to greatly increase the smoothness of the resultant coating. Nickel sulphate and cobalt sulfate usually are not dcsir+ able because they build up in the bath and a high level of sulfate is apparently harmful to the resultant coating. In any event, the nickel and cobalt increase smoothness and improve the plating in low current density areas by s! extending the plating range and the nickel by evening out the color. Likewise, nickel apparently increases the efficiency of plating in the low current density areas. Other metals, which may be advantageously added as soluble salts, are copper and cadmium as well as traces of lead and thallium. However, these metals are not as effective as nickel or cobalt. In general, the use of nickel and cobalt increases corrosion resistance.

Returning to the advantage of using the bath of Table I, upon the addition of the reaction product of dicy and formaldehyde (which preferably has an average molecular weight range of about 2000 to 8000 or 10,000) the deposited metal evens out and brightens up the normally poor deposits in high current density areas. This is one of the main advantages of adding the reaction product of dicy and formaldehydethe improvement of deposits in high current density areas and making the deposits bright, even and dense.

In a manner similar to Table I, Table II below sets forth the preferred and general ranges of amounts of ingredients in a typical white brass or zinc-copper alloy plating bath: a

1 Percent by volume of bath. 2 Percent determined by trial.

As indicated above, the amount of reaction product of dicy and formaldehyde in a zinc alloy plating bath should be preferably as much as 0.05% by volume in order to get a dense, fine grained, low porosity and bright deposit.

The above described bath is generally used at a current density of about 20-130 amperes per sq. ft. The operating temperatures of the bath generally range from 60 to 145 F. As is known in the art, in the temperature range between about 60 to 90 F. and above 124 F. the anodes are not polarized and thus, these temperatures are preferred for copper-zinc alloy cyanide plating baths.

In the presence of the reaction product of dicy and formaldehyde, the copper-zinc alloy plated is more dense, finer grained, less porous, brightened and even leveled somewhat. Using the reaction product of dicy and formaldehyde in the bath of Table II, white brass can be plated bright on metal surfaces such as steel and the like with no limitation on thickness. For instance, a layer 0.003 in. thick that takes 1 hour to plate can be just as bright as a layer plated in minutes. Under a microscope, before the reaction product and dicy and formaldehyde is put in the bath the white brass deposit has numerous scattered pits or particles over the surface. The addition of the reaction product of dicy and formaldehyde reduces markedly and nearly eliminates this pitting or scattering of particles over the surface. After the reaction product is added, the resultant coating is more alloyed, evener and looks more fused.

Another feature of the use of 'the reaction product of idicy and formaldehyde is that it permits the bright plating of sandwich layers of bright zinc and bright copperrich layers as well as white brass. Also, as discussed in the case of the zinc bathof Table I, in a similar manner, the reaction product of hexarnethylene tetramine and salicylic acid may be used in amounts of /3 to 3% by volume of bath (or about V2 to 4 02/ gal.) to stabilize the white brass bath illustrated in Table II'.

In general, as the amount of reaction product of dicy and formaldehyde is increased in the brass bath of Table II, the low density areas tend to be copper-rich instead of zinc-rich.

The following examples are intended to illustrate the present invention and not to limit it in any way.

Example 1 A zinc plating bath for the electrodeposition of zinc was prepared from the following ingredients.

Ingredients: Oz. per gal. Zinc cyanide 8 Sodium hydroxide 10 Sodium cyanide 4 Reaction product of dicy, formaldehyde and boric acid .01

Zinc was plated from the above bath using a current density of 40 a.s.f. and a temperature of 88 F. The resultant plate was bright and ductile and had improved corrosion resistance. The smoothness and evenness was very good even in the low and high current density areas.

Example 2 A white brass plating bath was made according to the formulation that follows.

Ingredients: Oz. per gal. Zinc cyanide 5 Copper cyanide 2.4 Sodium cyanide 7.8 Sodium hydroxide 4.5 Reaction product of dicy, formaldehyde and boric acid 1 0.1

1 Percent by volume of the bath or about 0.15 oz./per gal.

The resultant bath was heated to 82 F. and white brass plated therefrom for 60 minutes using a current density range of 60 a.s.f. The resultant plated coating was bright, dense, fine grained, and markedly low in porosity.

Example 3 A white brass plating bath was made according to the formulation that follows.

Ingredients: Oz. per gal. Zinc cyanide 5 Copper cyanide 2.4 Sodium cyanide 7.8 Sodium hydroxide -i 4.5

Reaction product of dicy, formaldehyde and boric acid 1 0.1 Nickel formate 0.05

1 Percent by volume of the bath or about 0.15 oz./per gal.

50 The resultant bath was heated to 82 F. and white brass r plated therefrom for 60 minutes using a current density range of 60 a.s.f. The resultant plated coating was bright, dense, fine grained, and low in porosity; the final coating being even smoother than the coating of Example 2 and slightly improved in the lower density areas. In contrast to this, a coating plated from this formulation (except that no reaction product of dicy and formaldehyde was used) was not bright, poor in surface regularity and relatively brittle.

Example 4 A bath was prepared using the same ingredients set forth in Example 2 except that a reaction product of hexarnine and salicylic acid was added in an amount of 2% by volume of the bath. The reaction product was produced by reaction of hexamine and salicylic acid at F. for 24 hours in an aqueous solution at a pH of 4.5 and the reaction mixture thereafter further reacted with potassium hydroxide to provide a pH of 9 /2. In general, the above reaction product can be made by reacting about 1 to 4 moles of salicylic acid and 1 mole of hexamine at a temperature of about 125 to 190 F. and a pH of about 2 /2 to 5 /2 for at least 4 hours and thereafter reacting the reaction mixture with about 2 to 4 moles of an alkali hydroxide to provide the final reaction product having a pH of about 8 to 12 and preferably about 9% to 10 /2.

The resultant bath was very stable, resulting in an economical bath. The resultant plated White brass coating was bright, dense, low in porosity and improved in corrosion resistance.

In the above examples, other suitable reaction products of dicy and formaldehyde previously described may be substituted for the particular reaction product of dicy and formaldehyde used in the working examples to provide similar results. In all the zinc and zinc-alloy plating baths, such as illustrated in the examples, the use of the reaction product of 1 mole of dicy and 3.5 to 5 moles 'of formaldehyde, particularly with 0.1 to 1 mole of boric acid, as the brightening agent, provides a denser deposit with an improvement in ductility as well as a reduced rate of corrosion. As an equally useful alternative as previously indicated, the polymer produced by reacting about 1 mole of dicy with about 0.1 to 3 moles of formaldehyde and about 4 to 10 moles of formic acid can be substituted for part or all of the reaction product of dicy and formaldehyde used in the working examples, to provide equivalent results.

In a similar manner, the sodium hydroxide used in the above examples can be substituted by another alkali metal hydroxide such as potassium hydroxide; likewise, in Examples 1 to 4, an alkali metal cyanide such as potassium cyanide can be substituted for all or part of the sodium cyanide to provide equivalent results.

What is claimed is:

1. An aqueous plating bath of the alkaline cyanide type for depositing a metal comprising zinc, the bath containing as a brightening agent about 0.005 to 2.5% by volume of a reaction product of about 1 mole of dicyandiamide, about 3.5 to 5 moles of formaldehyde, and about 0.1 to 1 mole of boric acid, the reaction products being soluble in cold water and non precipitating even on extreme dilution of aqueous solution, and the reaction product having a pH of about 7 /2 to 8 /2.

2. An aqueous plating bath of the alkaline cyanide type for depositing a metal comprising zinc, the bath containing about 0.005 to 3.0% by volume of a reaction product of (1) mixture of about 1 mole of dicyandiamide and about 3 to 6 moles of formaledhyde and (2) a mixture of about 0.1 to 3 moles of formaldehyde and about 1 to 4 moles of formic acid, the reaction product being soluble in alkaline solution.

References Cited by the Examiner UNITED STATES PATENTS 2,411,397 11/46 Walker. 2,451,426 10/48 Bair et al. 2,621,152 12/52 Hoifman. 2,852,490 9/58 Sellet et al. 260- FOREIGN PATENTS 461,074 11/49 Canada.

JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, MURRAY TILLMAN, Examiners. 

1. AN AQUEOUS PLATING BATH OF THE ALKALINE CYANIDE TYPE FOR DEPOSITING A METAL COMPRISING ZINC, THE BATH CONTAINING AS A BRIGHTENING AGENT ABOUT 0.005 TO 2.5% BY VOLUME OF A REACTION PRODUCT OF ABOUT 1 MOLE OF DICYANDIAMIDE, ABOUT 3.5 TO 5 MOLES OF FORMALDEHYDE, AND ABOUT 0.1 TO 1 MOLE OF BORIC ACID, THE REACTION PRODUCTS BEING SOLUBLE IN COLD WATER AND NON PRECIPITATING EVEN ON EXTREME DILUTION OF AQUEOUS SOLUTION, AND THE REACTION PRODUCT HAVING A PH OF ABOUT 7 1/2 TO 8 1/2. 